In recent years, there has been growing interest in deploying extended bridges (i.e., networking systems that make use of Institute of Electrical and Electronics Engineers (IEEE) 802.1BR Port Extension technology) for various applications like campus networks, virtualized data centers (VDCs), virtualized storage area networks (V-SANs), and so on. In an extended bridge (also known as a “virtual chassis system/topology”), controlling bridge (CB) nodes are responsible for configuration and control of Port Extender (PE) switching nodes. The CB nodes are often implemented using higher-end networking hardware (e.g., routers/switches) with greater traffic processing capabilities, while the PE nodes are often implemented using small to medium-sized low-power hardware that need to be efficient in terms of energy consumption and processing capabilities.
The PE nodes are generally connected in a tree topology with a CB node being the root of the tree. The leaf-level PE nodes are known as edge PE nodes and the PE nodes at tree branch points are known as transit PE or cascade PE nodes. The leaf-level PE nodes provide services to various end hosts or virtual machines (VMs) in VDCs. For scaling purposes, an extended bridge may include multiple PE trees, each rooted under a separate CB node, where the CB nodes themselves may be connected with each other in the form of a ring, mesh, or some other topology. Such an extended bridge topology with multiple rooted PE trees is sometimes referred to as a PE forest.
The IEEE 802.1BR standard requires that PE nodes be configured and controlled from a single point of management. Thus, in an extended bridge, a single CB node is generally designated as a master CB node that is responsible for configuration management of all other CB nodes and all PE nodes in the bridge. The master CB node is often heavily loaded compared to other CB nodes, since the master CB node is also responsible for running various control protocols, such as IGP routing (OSPF, IS-IS), BGP routing, security key distribution protocols, multicast routing, RSTP, MSTP, network management agents (SNMP, CLI, NETCONF, etc.), and the like. Accordingly, to ensure a high level of network quality of service, service availability, and overall performance and throughput, it is important that the master CB node is appropriately elected from among the eligible CB nodes so that the elected master has sufficient resources and processing capabilities to perform optimal forwarding of user traffic with service level agreement (SLA) guarantees.